1. Field of the Invention
The present invention relates to a sealing structure for a cylinder and a cylinder head, which is significantly effective for a reciprocating type internal combustion engine in which a cylinder and a cylinder head are detachably connected with each other through a gasket and an assembling method thereof.
2. Description of Background Art
In a reciprocating type internal combustion engine in which a cylinder and a cylinder head are detachably connected to each other, a gasket is interposed between the cylinder and the cylinder head for air-tightly sealing the cylinder and the cylinder head. Examples of gaskets include a semi-metallic gasket in which an outer surface of a plate-like substrate, formed of incombustible fibers such as asbestos, is covered with a thin metal sheet, and a metal gasket in which one or plural beads are concentrically formed along an opening, corresponding to a cylinder bore, formed in a thin metal sheet. See Japanese Utility Model Laid-Open No. Hei 5-73360.
A further proposal has been made for a reciprocating type internal combustion engine in which an annular groove having a larger diameter than a cylinder bore is concentrically formed in an end surface of a cylinder, and a metal-made endless ring whose cross-section is circular is fitted in the annular groove. See Japanese Utility Model Laid-Open No. Sho 59-60365.
The metallic gasket which requires plural types of raw materials is complicated in its structure. Therefore, the productivity of manufacturing is low and the cost is high. Further, since the substrate is not a thermally good conductor, heat of the cylinder head is hard to be transmitted to the cylinder so that the side wall surface of the cylinder head of the combustion chamber rises in temperature.
The metal gasket made of a thin metal sheet described in Japanese Utility Model Laid-Open No. Hei 573360 requires a plurality of sheets, as shown in Japanese Utility Model Publication No. Hei 6-37238, in order to secure a sealability, making it difficult to reduce the cost. In order to increase the fastening force of fastening bolts for fastening the cylinder and the cylinder head to each other in an attempt to adapt to the high output ratio of the internal combustion engine, there was a limitation in flatness of a gasket surface and accuracy in dimension of parts due to an increase in fastening strain.
The semi-metallic gasket as well as the thin metal made metal gasket require rigidity for the mating surface between the cylinder and the cylinder head. As a result of this, the wall-thickness of each of the cylinder and the cylinder head increases, making it difficult to reduce the weight of the internal combustion engine.
In the gasket described in Japanese Utility Model Laid-Open No. Sho 59-60365, the deformation of the endless ring caused by the diametrical compressive force applied to the peripheral surface of the metal-made endless ring is relatively large in the initial state but as the deformation progresses, the deformation increasing amount rapidly lowers. Therefore, an unevenness of a diameter of the endless ring, an error in depth of the annular groove, and a deviation of a planeness of the contact surface between the cylinder and the cylinder head cannot be absorbed sufficiently by the deformation of the endless ring. The contact surface between the cylinder and the cylinder head cannot be sealed positively unless the processing accuracy of the contact surface between the cylinder and the cylinder head is maintained at a high level.